When a patient suffers from an ischemic event, the blood supply to tissues and organs distal to the blockage or occlusion is significantly diminished. The resulting deprivation of oxygen increases the risk of necrosis of the tissues and organs. Generally, a patient suffering an ischemic event is treated by minimally invasive catheterization, such as for example percutaneous transluminal coronary angioplasty (PCTA). PCTA is employed to dilate the ischemic blockage and to restore the blood supply to the tissues and organs. Rapid restoration of blood flow after an ischemic event minimizes the duration of insufficient oxygenation to the tissue and organs, and therefore optimizes tissue and organ survival. However, it has now been found that restoring blood supply in a rapid and consistent manner results in reperfusion injury. A shock to the tissues and organs from rapid oxygen re-saturation and abrupt changes to pH level in the tissue can results in an overall increase in the infarct size.
Reperfusion injury results from the rapid opening of a blood vessel such as those of the coronary, peripheral, and/or cerebral vasculature. For example, the rapid opening of an artery of the heart during a ST-Elevation Myocardial Infarction (“STEMI”), or an artery to the brain (ischemic stroke), or an artery to the other vital organs such as the kidney or liver or other tissues of the body sometimes causes ischemic injury in myocardial, cerebral, peripheral and spinal infarction, for example.
One method to reduce or prevent the occurrence of reperfusion injury is a technique known as postconditioning. Postconditioning is a method during which the blood flow in the infarcted artery is stopped and started for multiple cycles immediately after re-opening of initial flow from the STEMI. This re-opening of flow can be either before or after angioplasty, with or without placement of a stent. Currently, physicians typically use an angioplasty catheter to perform postconditioning. However, the use of an angioplasty catheter is not optimal. For example, the angioplasty balloon is not configured to quickly occlude flow. Instead, the angioplasty balloon is designed to carefully create a new, circular lumen. Additionally, the typical angioplasty balloon is non-compliant, meaning it is designed and/or made of a material that is meant to be inflated with a range of pressures, while not significantly changing its outer diameter size. A typical non-compliant angioplasty balloon becomes circular at approximately 4 atmospheres of pressure. As the balloon pressure is increased, the outer diameter grows very little even as pressure is increased to 14-18 atmospheres. Such characteristics can be drawbacks for postconditioning. Further, an angioplasty balloon is typically designed to open a stenosis or blood vessel along a lesion, rather than just occlude flow. Thus, the length of an angioplasty balloon is generally between 8 mm to 40 mm, while an occlusion balloon could be shorter.
Another major drawback to using an conventional angioplasty catheter for postconditioning is that prior to use, the physician must measure the artery, for example, by fluoroscopy, then size the balloon both for length and diameter, retrieve an appropriately sized balloon from inventory, and then go through various steps to prepare the balloon such as removing the air trapped within the balloon before filling the balloon with saline/contrast mixture. Thus, using the angioplasty catheter with the angioplasty balloon suffers from inefficiencies. Further, the angioplasty catheter typically must be manually actuated to both inflate and deflate the balloon. For example, the use of an angioplasty catheter for postconditioning usually requires rapid rotation of a screw piston in order to deliver the fluid in a controlled manner, while watching the pressure gage of an Indeflator. Inflation of the balloon to a circular size can require 10-20 twists of the Indeflator in order to expand the balloon. During deflation, the Indeflator is normally directly unlocked and rapidly deflated. If a controlled deflation is required, then the Indeflator can be manually screwed down to a lower pressure. Physician to physician variability will directly ensue, meaning that over the course of multiple inflations and deflations, there will be a great variability in the rise and fall of blood flow in the artery. Normalizing the blood flow, i.e. the rate of inflation, pressure of inflation, and rate of deflation across physicians can be critical to the efficacy of postconditioning. In addition to the cumbersome nature of actuating inflation and deflation of the angioplasty catheter, the speed of inflation is limited by the physical capability or limitations of the treating physician to rapidly rotate the screw piston. Given that many sequential inflations and deflations are needed during a postconditioning, use of an angioplasty catheter has many drawbacks. As a result much time is lost in the process of using a conventional angioplasty catheter for postconditioning.
Use of a conventional angioplasty catheter can also result in significant operator-to-operator variability in inflation time, pressure of balloon, size of balloon, and deflation time. A system which normalizes the inflation time, pressure, size and deflation time is required, while still allowing operator control of the duration of inflation. Lastly, angioplasty balloons, especially rapid exchange balloons, do not have any means to deliver drug distal to the balloon without the added steps of removing the rapid exchange guidewire and replacing the rapid exchange guidewire with an over-the-wire guidewire.
Therefore, a need exists for a system that is capable of restoring blood flow after an ischemic event in an intermittent and gradual fashion with ease and efficiency, while allowing the option of drug delivery distal to the balloon over a standard length guidewire. Further, there remains a need for an ischemic postconditioning system comprising a catheter and a fluid circuit to control and modulate flow of inflation fluid to and from a balloon wherein balloon can be semi-automatically inflated and deflated. Additionally, a need also exists for safety measures which prevent over inflation of the balloon, thus mitigating the risk of balloon rupture and vessel injury, as described below. The disclosed subject matter includes a method and apparatus for performing ischemic postconditioning in a much shorter time and at significantly reduced risk to the patient than is possible with prior art technology.
Additionally, as mentioned above, PCTA is employed to dilate the ischemic blockage and to restore the blood supply to the tissues and organs when a patient suffers from an obstructed blood vessel, typically as a result of atherosclerosis. During PCTA, an empty (deflated) and collapsed balloon disposed on a catheter is usually passed into the narrowed location of the blood vessel and then inflated to a fixed size. Inflation of the balloon at the narrowed location of the blood vessel compresses the obstruction to open up the blood vessel for improved flow. During the angioplasty procedure, the physician is required to determine whether the balloon is inflated by reviewing the balloon on a monitor or screen usually away from the patient undergoing the treatment. Thus, the physician must be careful enough to maintain the catheter at the lesion and take his view away from the patient to view the screen to make the determination if the balloon is inflated or depend on another to view the monitor. Thus, there is a need for an easy to use balloon catheter having an indicator to indicate to the physician when the balloon is inflated in a manner assures the physician the balloon is inflated without being required to turn away from the patient or make the judgment from a monitor.